1. Field of the Invention
The present invention relates to a near-field antenna and, more particularly, to a near-field antenna for item-level tagging, which is capable of recognizing a large quantity of approaching tags in a bundle using a near field.
2. Discussion of the Related Art
An Ultra High Frequency (UHF) band Radio frequency IDentification (RFID) application field is expanding from the tagging of a pallet, case, or box unit to item-level tagging. In general, for item-level tagging, the RFID technique of a High Frequency (HF) band was preferred, but has problems, such as the size and price of a tag, the tagging distance, the data processing speed, and compatibility with the existing UHF band RFID standard.
Unlike the RFID technique of an HF band using a magnetic coupling method, the RFID technique of a UHF band using a back-scattering method of electromagnetic waves is advantageous in that it has a relatively long tagging distance and thus has been widely used in the distribution of the pallet unit and the materials management of the box unit.
However, the RFID technique of a UHF band shows performance that the tagging ratio sharply drops in the item-level tagging (ILT) application field in which a large number of items are clustered together because of the scattering, interference, etc. of electromagnetic waves. In order to overcome the shortcoming of the UHF band RFID technique in the item-level tagging, active research is being carried out on an RFID antenna technique using a near field in the UHF band.
If a UHF band far-field is used for the tagging of the pallet or box unit and a UHF band near field is used for a large amount of item-level tagging, not only the tagging of the pallet or box unit, but also the item-level tagging is possible using the UHF band RFID technique.
Unlike the HF band RFID technique using the magnetic coupling method, a technique using a UHF band near field is advantageous in that the magnetic coupling method and the electric coupling method can be properly selected according to an item to which a tag is attached and service environments.
However, the UHF band near-field RFID reader antenna has to be designed based on a different concept from that of the existing far-field antenna. That is, the UHF band near-field RFID reader antenna has to be designed by taking an item-level tagging environment, a tag attachment location, and a required near-field distribution into consideration. Furthermore, since near-field communication is performed according to the coupling method between a reader antenna and a tag antenna, the structure of the tag antenna has to be taken into consideration in the design of the reader antenna.
A conventional technique pertinent to the UHF band RFID reader antenna basically includes a far-field application of a microstrip patch antenna form. Furthermore, an RFID smart shelf application is chiefly implemented using a loop antenna in the HF band.
In general, the RFID smart shelf may have a variety of sizes and shapes according to the application field. Accordingly, the size of the reader antenna mounted on the smart shelf has to be able to be easily changed according to a change of the size and shape of the shelf according to application. In other words, the reader antenna mounted on the shelf has to be able to be easily extended and reduced according to a change of the shelf structure (i.e., size and shape).
That is, the reader antenna for the RFID smart shelf has to have a uniform field distribution without a fading zone so that a number of items on the shelf can be stably recognized and to have a structure in which the antenna size can be easily extended and reduced according to a change of the shelf structure.
However, there are a lot of difficulties in designing an RFID reader antenna having the above characteristics using a conventional HF band antenna technique and a conventional antenna technique of a UHF band.